Regulation of gene expression is critical for cellular and organismal development, and often plays an important role in expression of heterologous recombinant proteins. Toward development of regulated expression vectors for filamentous fungi that will minimize materials cost and manipulation of the fermentation culture, we propose to define cis-acting, blue light responsive regulatory elements and to incorporate them into expression vectors. As a model, we propose to subclone sequences of the al-1 locus of Neurospora crassa and demonstrate that they will confer blue light regulation to promoters not normally exhibiting this regulation. Bovine chymosin will be used as the heterologous reporter sequence and gene product. If successfully developed, expression of heterologous products normally toxic to fungi could be prevented by fermentation in the dark and elicited by merely switching on illumination.